It is sometimes difficult to get a perspective on things that one is intimately involved in, and grammar is no exception! It is not true that grammar is becoming technically simpler. It is true that grammar of the past, in as much as it is different from today, looks more complicated, and that the grammar employed in text messages on mobile phones seems to suggest that the grammar of the future will be more simplistic than the one we know is right.

Grammar is about the construction of discourse. It is easy to look on a very obvious exhibition of grammar, like inflexions in Old English, and conclude that Old English grammar is more complicated than that of Modern English (an Anglo-Saxon might disagree). However, Modern English has introduced nuances into the language which are imposible in Old English, and all through little grammar tweaks. One major difference in the history of English grammar is the ability of many words to be employed in different word classes; the other major difference is the meaningful use of word order. The use of the progressive aspect construction in English and the use of do is a primary verb are two other complications of Middle and Modern English.

First problem: what is grammar? If we understand it as form history, we get reconstructions that are some kind of mean value of Sanskrit, Latin, the oldest Greek and a few others. That means, studying PIE we look at some six noun cases (normally nominative, accusative, genetive, dative, locative and instrumental). For verbs, there are two major groups: the perfective and the imperfective ones.

I don't know to what extent, if any, there is research in PIE syntax. I get a feeling that comparative linguistics in most countries has difficulties in attracting funding, because it is difficult to prove that it generates benefits other than making the researchers happy. There is no way that you can trick the CIA into funding PIE research, in the way when you create software that can "parse" Moby Dick in 9 and a half seconds. ("Computer does something-or-other to Moby Dick -- in 9.5 seconds" at http://www.languagelog.com/)

Grammar seems to get simpler over time. How did the earlier complex grammars come about from presumably the very simple grammars used with man's first grunts?

I have tried to look into theories on how language emerged. I haven't so far been able to build a theory if my own, but I think it is much more complicated than that it started as just grunts.

And how would we measure simplicity? The number of forms for a noun or a verb might be one kind of measure. The verb in Hindi has very few forms, perhaps even fewer than English verbs (there are only five irregular verbs, and they are regular as well, but in another way). Looks simple indeed. But do they have other ways to complicate verbs!! In most Hindi sentences, there is a host of verb forms at the end, indicating subtle nuances like, was the action sudden or gradual, did it mainly benefit the actor or the acted-on, was it abrupt or continous, was it completed or not, ...

I'm sorry that I can't come up with a better answer, or even ideas for research to provide some kind of platform from which to go on. But I enjoy discussing those things, and that is more important to me, than for example acquiring a reputation for solving some linguistic problem.

Thanks Apo, thanks AlphaDictionary.
Geoffrey Sampson should be here, or maybe he is.
A very nice overview and just the sort of lead I've been looking for.

The question of language complexity seems to me to remain open.
Language cannot have started fully formed, so must have initially increased in complexity, whatever that means (as an aside, I cannot for the life of me see why it would have evolved with gender!). Has it got more or less complex since PIE? Has it just become 'richer'? Larger vocabulary, more ways of saying the same thing with subtle differences in meaning but simpler structure, no thees and thous and less gender, in English at least.

I don't think I've ever seen anything on PIE syntax: I imagine that it had fairly free word order, but that's difficult to recreate. PIE is an extapolation of related Indo-European languages back to some kind of reinvented, unified beginning. The more you look at PIE phonology and morphology, you realise that there must have been quite a few stages of development, and so PIE itself cannot be seen as one single stage in language evolution.

It is customary to think of PIE with six or so noun cases, but these may only have existed at a very late stage of development. It is also customary to think of PIE having three grammatical genders, but things may have been different at earlier stages. One widely accepted theory of grammatical gender in early PIE is that it had two genders: animate and inanimate. This would explain certain word pairs for things like fire and water in IE languages: animate fire/water does what it wants, inanimate fire/water does what I want. Whereas animate nouns could be singular or plural, inanimate nouns had a collective plural. Perhaps on contact with Afro-Asiatic languages, which seem to have had the masculine/feminine thing for longer, PIE developed its more customary sense of gender. Animate class became masculine gender and inanimate class became neuter gender. The feminine gender seems to have developed out of the inanimate collective plural! This explains for the case structure of Anatolian languages (more like the animate/inanimate classes), the word pairs, the use of a singular verb with neuter plurals in some IE languages, and the similarity of the feminine singular to the neuter plural.

The most ancient languages which were recorded in writing had very limited systems of grammatical subordination; some languages spoken by simpler, tribal societies today demonstrably are less evolved than modern European languages in this respect.

I find lots of problems just in these few lines. First, we can't be sure that the first lines in writing had any resemblance to the spoken language. They might very well have been some kind of shorthand, until the principles of writing evolved and got accepted and refined. On my shopping list, I write "2 milk", but what I would say is "I itend to buy two one-litre cartons of milk."

Second, some old writings seem to be simple because in some of them, there are few inflections. But like Garzo and yours truly have hinted at, it is difficult for us to find out what rules of syntax were working. They should have compensated for the apparent "simplicity".

And I most vehemently protest against the "less evolved" bit. The most complicated "systems of grammatical subordination" I've seen belong to "tribal" languages. Take for example the Papuan language Taiap, and how it renders "She hit the girl."
Guyi ror pokun.
gu- stem for the pronoun 'she'
-yi ergative case ending (marks the subject of a transitive verb)
ror 'girl'
p- p- ... -n: the subject is 3 p. sing.
-o- stem for the verb 'hit'
-ku-: the object is 3 p. sing. fem.
-n (see p-).

There are of course worse cases, but they are too difficult to reproduce in a post, with all their necessary relations to other words in the sentence.

And if you argue that less complex grammars are more evolved, you contradict the first sentence in the quote.

Grammar seems to get simpler over time. How did the earlier complex grammars come about from presumably the very simple grammars used with man's first grunts?

The old English grammars followed the pattern of Latin grammars. They had conjugations and spoke of subjunctives. They tried to fit English into the categories of a foreign language. That is why they were complicated; they did not make sense.The idea of not ending a clause with a preposition is an example of that kind of grammar.

English grammars started to make sense when they were developped from the observation of the English language as spoken and written.

The feminine gender seems to have developed out of the inanimate collective plural!

This has struck me. Which could be, if you know of any, the relationship between that fact and the way Arabic expresses the same inanimate plural? I feel there must be something...

I mean, constructing inanimate plurals with the feminine is too "illogical" a thing (i.e., not induced by how our world is) to be a simple coincidence. Do you think it could be a reminiscence in Arabic of that old plural? But, if so, why? Given that Arabic is not an IE language...